Survival of Verticillium dahliae in soil PublicDeposited

Descriptions

Three Oregon soil types (Chehalis silt loam (CSL), an alluvial
soil from the Willamette Valley; Ayre sandy loam (ASL), a volcanic
pumice soil from the Central high desert; and Klamath fine sandy
loam (KFSL), a basaltic mineral soil from the Klamath Basin) were
collected adjacent to fields which had been removed from potato production
due to Verticillium wilt caused by the soil-borne fungus
Verticillium dahliae kleb.
The soils were infested with V. dahliae inoculum composed of
individual microsclerotia (MS) or microsclerotia imbedded in stem
pieces (SPMS). The infestation level was 100,000 propagules/g
soil. The inoculum was derived by fragmenting and screening
field-infested potato stems.
Each infested soil type was transported to, and incubated at,
each of the above geographic locations. Changes in the V. dahliae
populations were studied over a five-year period. The inoculum
potentials of the surviving N. dahliae populations in soils which had been infested with 1000 propagules/g were bioassayed with eggplants
after five years.
V. dahliae microsclerotia freshly added to moist soils showed
an initial flush of sporulation with a subsequent population decline.
Population lows were reached after 71 or 256 days incubation, depending
on soil type and geographic location. After reaching lows
of 14-45 percent of the original population, all V. dahliae populations
showed gradual increases through the remainder of the five-year
test period. Final populations were 34-63 percent of the original
population.
CSL soil and the Corvallis environment exerted a strong influence
on V. dahliae sporulation. V. dahliae populations in all three
soil types infested with MS inoculum showed periodic population
fluctuations of up to four-fold at the Corvallis location through the
five-year study. ASL and KFSL soil types suppressed sporulation
of V. dahliae at the Redmond and Klamath Falls locations.
Organic matter breakdown and subsequent release of V.
dahliae propagules from stem piece inoculum was related to soil
type and geographic location. After 20 months incubation, organic
matter breakdown ranged from 7 percent in the CSL soil at the
Corvallis location to 88 percent in the ASL soil at the Klamath Falls
location. After five years incubation the inoculum potentials varied
with soil type and geographic location. Only 20 percent of the eggplants grown in the CSL soils from Redmond showed symptoms,
whereas 100 percent of the plants grown in the KFSL soil from the
Corvallis and Klamath Falls locations showed symptoms.
The three soil types at three levels of infestation were studied
over a 290 day period under controlled conditions of soil moisture
and temperature in the laboratory. Upon initial infestation with
microsclerotia there were population increases in direct proportion
to the level of infestation. Unlike the field experiments, no periodic
population fluctuations occurred during the 290 day incubation period.
The percent V. dahliae survival after 290 days was inversely proportional
to the initial infestation levels in the three soils, while
percent survival between soil types was in the order of CSL>ASL>KFSL.
A linear regression analysis of Verticillium wilt symptom
development in eggplants grown in the three soil types, infested at
three levels showed a significant difference between the lowest infestation
level and the two higher levels and also between soil types.
Symptom development in the KFSL soils were significantly slower
and less severe.
The number of infection loci/g root was not proportional to the
inoculum density in the soil. Infection loci/1000 propagules/g of
soil were 4.0 in KFSL soils and 2.4 in ASL soils. Eggplants grown
in V. dahliae infested soils showed increased fresh weights at each
increased infestation level.